1. Field of the Invention
Embodiments of the subject matter disclosed herein generally relate to methods and systems and, more particularly, to mechanisms and techniques for controlling a gas turbine.
2. Description of the Prior Art
Turbomachinery used, for example, in power plants or jet engines, are continuously evolving based on new discoveries and better materials. In addition, the manufacturers of these machines are under increased pressure to produce or improve the machines to be “greener,” i.e., to reduce the amount of pollution produced while operating.
Thus, there is ongoing research for lowering the exhaust emissions of turbo machineries especially considering the desire to use a wide range of gaseous fuels. Meeting these requirements becomes more and more difficult, particularly when considering the wide range of operation of these devices. An accurate turbomachine exhaust temperature control becomes, under these conditions, a relevant factor in order to develop successful applications.
One approach for lowering the pollution produced by a turbomachine is based on a paradigm of exhaust temperature versus compressor pressure ratio. In this regard, U.S. Patent Application Publication 2008/0243352, the entire content of which is included here by reference, describes that current control systems may execute scheduling algorithms that adjust the fuel flow, inlet guide vanes (IGV), and other control inputs to provide safe and efficient operation of a gas turbine. Gas turbine control systems may receive as inputs operating parameters and settings that, in conjunction with scheduling algorithms, determine turbine control settings to achieve the desired operation. Measured operating parameters may include compressor inlet pressure and temperature, compressor exit pressure and temperature, turbine exhaust temperature, and generator power output. Desired operating settings may include generator power output and exhaust energy. The schedules (e.g., exhaust temperature vs. compressor pressure ratio, fuel splits vs. combustion reference temperature, inlet bleed heat (IBH) vs. IGV, compressor operating limit line vs. corrected speed and inlet guide vane, etc.) are defined to protect the turbine against known operational boundaries (e.g., emissions, dynamics, lean-blow-out, compressor surge, compressor icing, compressor clearances, aero-mechanical, etc.) based on off-line field tests or laboratory data. The output of the schedules then determines the appropriate adjustment of the control system inputs. Typical control inputs managed by a control system may include fuel flow, combustor fuel distribution (which may be referred to as “fuel splits”), compressor inlet guide vane position, and inlet bleed heat flow.
FIG. 1, which is similar to FIG. 1 of U.S. Patent Application Publication 2008/0243352, illustrates an example of a gas turbine 10 having a compressor 12, a combustor 14, a turbine 16 coupled to the compressor 12, and a computer control system (controller) 18. An inlet duct 20 to the compressor 12 may feed ambient air to compressor 12. The inlet duct 20 may have ducts, filters, screens and noise abatement devices that contribute to a pressure loss of ambient air flowing through the inlet 20 and into inlet guide vanes 21 of the compressor 12. An exhaust duct 22 for the turbine directs combustion gases from the outlet of the turbine 10 through, for example, emission control and noise abatement devices. The amount of inlet pressure loss and back pressure may vary over time due to the addition of components and due to dust and dirt clogging the inlet 20 and exhaust ducts 22. The turbine 10 may drive a generator 24 that produces electrical power.
As described in U.S. Patent Application Publication 2008/0243352, the operation of the gas turbine 10 may be monitored by several sensors 26 designed to measure different performance-related variables of the turbine 10, the generator and the ambient environment. For example, groups of redundant temperature sensors 26 may monitor ambient temperature surrounding the gas turbine 10, compressor discharge temperature, turbine exhaust gas temperature, and other temperature measurements of the gas stream through the gas turbine 10. Similarly, groups of redundant pressure sensors 26 may monitor ambient pressure, and static and dynamic pressure levels at the compressor inlet and outlet turbine exhaust, at other locations in the gas stream through the gas turbine 10. Groups of redundant humidity sensors 26, for example, wet and dry bulb thermometers, may measure ambient humidity in the inlet duct of the compressor 12. Groups of redundant sensors 26 may also include flow sensors, speed sensors, flame detector sensors, valve position sensors, guide vane angle sensors, or the like, that sense various parameters pertinent to the operation of gas turbine 10. As used herein, “parameters” refer to items that can be used to define the operating conditions of the turbine, such as but not limited to temperatures, pressures, and gas flows at defined locations in the turbine.
Also described in U.S. Patent Application Publication 2008/0243352A, the fuel control system 28 regulates the fuel flowing from a fuel supply to the combustor 14, one or more splits between the fuel flowing into primary and secondary fuel nozzles, and the amount of fuel mixed with secondary air flowing into a combustion chamber. The fuel control system 28 may also select the type of fuel for the combustor. The fuel control system 28 may be a separate unit or may be a component of the main controller 18. The controller 18 may be a computer system having at least one processor that executes programs and operations to control the operation of the gas turbine using sensor inputs and instructions from human operators. The programs and operations executed by the controller 18 may include, among others, sensing or modeling operating parameters, modeling operational boundaries, applying operational boundary models, applying scheduling algorithms, and applying boundary control logic to close loop on boundaries. The commands generated by the controller 18 may cause actuators on the gas turbine to, for example, adjust valves (actuator 27) between the fuel supply and combustors that regulate the flow, fuel splits and type of fuel flowing to the combustors; adjust inlet guide vanes 21 (actuator 29) on the compressor; adjust inlet bleed heat; as well as activate other control settings on the gas turbine.
U.S. Patent Application Nos. 2002/0106001 and 2004/0076218, the entire contents of which are incorporated here by reference, describe a method and system for adjusting turbine control algorithms to provide accurate calculation of a firing temperature and combustion reference temperature of a gas turbine as the water vapor content in a working fluid varies substantially from a design value. These references disclose using turbine temperature exhaust and turbine pressure ratio for controlling the firing temperature.
However, the traditional methods and systems are limited in their capability of controlling the gas turbine and accordingly, it would be desirable to provide systems and methods that obtain a more accurate firing temperature control, and/or a more accurate combustion parameters control, and/or a more accurate exhaust emissions control.